Warning! SPOILERS for Black Panther to follow. See it first, it's good!
The Marvel Cinematic Universe is full of fun and interesting characters beyond just the main heroes, and Black Panther is no different. Ryan Coogler's film features many new and exciting characters, some of which we're excited to see return in a more prominent role. One side character that previously appeared in Captain America: Civil War, but took on a bigger role in Black Panther, was Martin Freeman's Everett Ross. The character takes on a much more active role in Black Panther and in so doing, the Everett Ross of the MCU further differentiated himself from his comic book inspiration. In the comics Everett Ross is a timid and straight-laced kind of guy and as Martin Freeman explained, he wanted something different for the character's on-screen depiction, saying:
I, to be honest, wasn't massively keen to play that. I certainly wasn't massively keen to play that in the context of Black Panther. Just because I think the trope of a nervous white guy, cool black guy, we've seen it a million times before breakfast. So yeah, I wasn't mostly keen. Fortunately, Ryan [Coogler] and Nate Moore weren't massively keen either on that. So we talked a lot about what he might be. It's not like I shaped Ross into what he ended up being. I think, you know, that was [who] he was going to be. But I definitely threw my 10 cents in as far as who he might be.
Martin Freeman is correct that the "nervous white guy around a cool black guy" character has been done to death, so I can understand why he wouldn't want to play it that way, as he explained to Den of Geek. The actor already played the perpetually nervous white guy before in the first season of the excellent Fargo TV series. It sounds like Martin Freeman didn't have a lot of input, but Ryan Coogler wound up taking the character in a different direction anyway, and one that was less "nervous nelly" and more "guy in a bit over his head."
Agent Ross isn't exactly cool in Black Panther, at least not with Shuri, T'Challa and Nakia as around, but he is a character with agency who proves himself capable and useful. Although he isn't quite as nervous as his comic book counterpart, he is clueless at times about Wakanda and its technology, and is obviously concerned about the implications of Wakanda's power on the global stage. He is very much out of his element once the plot shifts back to Wakanda and is playing a lot of catch up, which is understandable. Plus, there was no way to prepare for a teenage girl calling him a 'colonizer.'
In Black Panther, Martin Freeman's Agent Ross strikes a nice balance between the sweaty-palmed bureaucrat of the comics and a capable character who is a real asset to the team. Part of this stems from his different background in the film universe. Everett Ross is a frequent presence in the Black Panther comics where he worked as a State Department liaison to T'Challa and Wakanda, but in the MCU, he is a CIA operative who works in a counter-terrorism capacity. He may not get a fancy suit or powers, but that is a badass job. That makes him far better suited to MCU adventures than his comic book counterpart. This shows when in the film's third act, Agent Ross proves an integral part of the team to reclaim the Wakandan throne as he stops the advanced tech from leaving the country.